1. Field of Invention
The present invention relates to an interpolation FIR filter, and more particularly relates to an interpolation FIR filter used in a scaling engine.
2. Description of Related Art
The polyphase FIR (Finite Impulse Response) filter is the key component of the scaling engine. The scaling engine is applied on the image processing to optimize the image. Therefore, the FIR filter is arranged to deal with the pixel of an image. The traditional FIR filter is operated according to the equation described bellow:pixel=[(pixel A)×(coefficient A)+(pixel B)×(coefficient B)/2m  (1)
wherein                the ‘pixel’ is the new pixel value of the processing pixel after the FIR filter's operation;        the ‘pixel A’ is the pixel value of the first pixel next to the processing pixel;        the ‘pixel B’ is the pixel value of the second pixel next to the processing pixel;        the ‘coefficient A’ is the interpolation coefficient of the ‘pixel A’;        the ‘coefficient B’ is the interpolation coefficient of the ‘pixel B’; and        the interpolation coefficient is a m-bit binary number.        
FIG. 1 is an interpolation FIR filter of the prior art. The traditional FIR filter operated according to the equation described above has two multipliers 110 and 120, an adder 130, and a divider 140. The multiplier 110 deals with the pixel value of pixel A and coefficient A; and the multipliers 120 deals with the pixel value of pixel B and coefficient B. Therefore, the traditional FIR filter needs two memory devices (such as ROM) to store this interpolation coefficient A and coefficient B.
The ROM tables stored the interpolation coefficients are big parts of the traditional FIR filter. Therefore, a FIR filter with fewer memory devices is needed.